The present invention relates to a centrifugal separator used in fields of medical science, pharmaceutical science, biogenetics, chemical engineering, food manufacturing, manufacture of pharmaceutical products, and the like, and, more particularly, a centrifugal separator having an angle rotor capable of increasing an amount of liquid specimen which can be processed at a time.
A centrifugal separator used for separating a liquid specimen includes: a rotor that holds a plurality of specimen containers containing liquid specimens in specimen container holding cavities equally arranged along a circumference of the rotor; and drive means, such as a motor, that rotationally drives the rotor in a rotor chamber. The centrifugal separator rotates the rotor in the rotor chamber under atmospheric pressure or reduced pressure at high speed, thereby centrifugally separating liquid specimens in the specimen containers to collect objects. The centrifugal separator that is a primary subject of the present invention achieves a maximum rotational speed of the order of 5,000 to 30,000 rpm and can employ as usage rotors having various specifications.
Liquid specimens include various liquids, such as blood components, a culture solution for a fungus body or a virus, living-body components like liquids including DNA and RNA, polymer suspension, ink, and food processing fluids. These liquid specimens are subjected to centrifugal separation for various purposes during processes, like a research, a test, an inspection, and manufacture.
A known rotor for use in a centrifugal separator is described in connection with; for instance, JP2008-119649A. FIG. 21 shows a side view of a related-art angle rotor 130, and a left half of the drawing shows a cross section of the rotor. In FIG. 21, a plurality of specimen container holding cavities 132 (only one of them is illustrated in FIG. 21) are made at equal angular pitches along a circumference of the rotor 130. A specimen container 150 filled with a liquid specimen is inserted into each of the holding cavities 132. A rotor cover 140 is attached to an opening in an upper surface of the rotor 130, and the rotor cover 140 is fixed to a rotor body 131 by means of a handle 141, whereby an interior of the rotor 130 is sealed. A drive shaft hole 131A is formed in a lower portion of a center shaft of the rotor body 131. The drive shaft hole 131A is attached to a drive 112 connected to a drive shaft (not shown) of the centrifugal separator. The rotor 130 is rotated at predetermined speed by drive means.
FIG. 22 is an oblique perspective view showing a shape of the specimen container 150 that has been known in connection with JP2004-290746A and that is to be attached to any of the holding cavities 132 of the related-art rotor body 131. In the centrifugal separator using specimen containers with caps, a body 151 of the specimen container 150 is columnar. A screw cap 152 is attached to an upper portion of the body 151, to thereby seal a liquid specimen. The cap 152 is made up of an inner cap and an outer cap. The specimen container 150 is usually embodied as a molded article using plastic materials, such as polypropylene, polycarbonate, polystyrene, and polyethylene terephthalate. The specimen container is usually reused again and again in many cases. Each of the body 151 and the cap 152 assumes a square transverse section. When inserted into the holding cavity 132 of the rotor 130, the body and the cap can be attached to the rotor at an arbitrary position with little concern for a rotational position determined with reference to a longitudinal center axis of the specimen container 150. The word “transverse plane” used herein means a cross-sectional plane perpendicular to the vertical direction of the specimen container.
In relation to the specimen container 150 with a cap that is employed in the angle rotor 130, specimen containers having a capacity of the order of 2 ml/container to a capacity of the order of 1000 ml/container have already been commercialized as usage. There are also available various rotors in which the number of specimen container holding cavities 132 made in the rotor 130 ranges from four/rotor to 20/rotor, or thereabouts. The rotor 130 is generally manufactured from a light-weight, high-intensity aluminum alloy, a titanium alloy, a carbon fiber composite material, and the like. In relation to the rotor 130, commercialized rotors include; for instance, a rotor capable of containing six specimen containers each of which has a capacity of 30 ml (hereinafter called a “300 ml-by-six”); a 500 ml-by-six rotor; and large-capacity angle rotors, such as a 1000 ml-by-four rotor, a 1000 ml-by-five rotor, and a 1000 ml-by-six rotor. An increase in the size of the rotor body proceeds with the changing times. Moreover, the size of the rotor body also becomes greater as the capacity of the specimen container becomes greater. In the case of for instance, rotors whose specimen containers have a capacity of 300 ml to 1000 ml, the maximum diameter of a rotor body is in excess of 300 mm.
Incidentally, removal and attachment of a rotor to a centrifugal separator is performed by an operator. Manufacturers of centrifugal separators including the present patent applicant have made efforts to lessen a weight of the rotor and enhance operability of the same by making structural contrivance to the rotor. Further, attempts have also been made to increase a capacity of a specimen that can be subjected to centrifugal separation at a time, by increasing the size of the specimen container. In recent years, a centrifugal separator using a large-capacity 1000 ml-by-four angle rotor has widely been used. Moreover, a disclosed specimen container is equipped with a cap, such as that described in connection with JP2004-290746A in which through holes 152A for ejection purpose are made in the cap 152, thereby facilitating ejection of the specimen containers and preventing leakage of a specimen in the course of centrifugal separation.
In order to efficiently collect an object from a liquid specimen during a centrifugal separation process, a common practice is to increase rotational speed of the rotor so as to increase centrifugal acceleration imparted to a liquid specimen and enhance a centrifugal effect, thereby accelerating spin-down of the object, increasing a collect rate, and increasing an amount of specimen capable of being processed at a time. A reduction in expenses to be incurred in centrifugal separation operation is important in inexpensively constructing a specimen container and a centrifugal separator including a rotor. However, it is also important to increase an amount of specimen capable of being subjected to centrifugal separation at a time, thereby increasing a yield.
In order to subject a large quantity of liquid specimen to centrifugal separation at a time, it is effective to increase the number of specimen containers used in the rotor and capacities of the respective specimen containers. However, in order to increase the capacity of the related-art columnar specimen container without modifications, it is necessary to increase an outer diameter or height of the body 151. As a result, the specimen container holding cavity of the rotor comes to interfere with adjacent holding cavities; hence, it is necessary to relocate the positions of the holding cavities in a radially distal direction (toward an outer circumference) from a rotation center. As a consequence, the diameter of the rotor itself increases, which in turn results in an increase in the weight of the rotor, thereby worsening worker's portability of a rotor and ease of detachment/attachment of a rotor to a centrifugal separator performed by the worker.
Further, an increase in the diameter of the rotor leads to an increase in air resistance (a windage loss) arising when the centrifugal separator rotates at high speed. Therefore, required countermeasures include an increase in power of a drive unit of the centrifugal separator and power of a cooling unit for cooling the rotor. An additional necessity is to increase the size of the rotor chamber (chamber) of the centrifugal separator in association with an increase in the diameter of the rotor. A footprint of the centrifugal separator increases, thereby raising a problem of an increase in the cost of the centrifugal separator.
During the course of resolution of these drawbacks, the present inventors focused an attention on presence of a constituent material (hereinafter called “pads”) of the rotor, which is a cause for an increase in weight, between adjacent specimen container holding cavities when the rotor including columnar specimen containers is viewed from above, and improvements have been made to minimize the pads. Further, during the course of achievement of improvements, it was found that the pads located in the vicinity of the outer circumference of the rotor became a cause for an increase in the weight of the rotor and that centrifugal load exerted on the pads became a cause for deterioration of strength of the rotor.